Re-platforming the core without losing a decade of loan history
The new platform is the easy part. The old data is where lenders get hurt.
Specialist lenders and building societies are modernising core systems in numbers — towards Mambu, nCino and their generation, away from platforms that have quietly run British lending since the Phoebus era. Vendor selection gets the board papers. The data gets a workstream named "migration" and a dangerous assumption: that it's a loading exercise.
Loan history is not a snapshot
A live mortgage is easy to move: balance, rate, term, borrower. What's hard is the decade behind it — payment histories, arrears events and their handling, forbearance arrangements, rate changes, fee reversals. Regulatory reporting needs it. Complaints handling needs it. Fair-treatment evidence under Consumer Duty needs it. And the new platform's data model almost certainly represents it differently from the old one.
Three decisions to make early
What moves, what archives. Not everything belongs in the new core. But "archive" must mean queryable-with-lineage, not a mothballed database nobody can read in 2031.
How history maps. Event-by-event translation between core banking data models is the highest-judgement work in the migration. It wants a written, versioned mapping specification an engineer signed — not tribal knowledge in a contractor's head.
How you'll prove it. Reconcile balances to the penny, obviously — but also reconcile the history: arrears status yesterday equals arrears status today, for every account. That's the test that catches the subtle mapping errors, and it's the evidence your next regulatory data request will lean on.
Got a cutover date? Tell us the source system, the target, and the deadline — we'll tell you within 48 hours whether we can hit it and what the Assessment will cost.
freddie@godwit.uk